J . Am. Chem. SOC.1991, 113, 3616-3618
3616 R
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1600 1400 1200 WAVENUMBER I cm-1
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change from anti of free cAMP to syn of CRP-bound CAMP. This result is consistent with those of 'H NMR studiesZoJ in solution but inconsistent with the structure of cAMP in crystalline cRP-c A M P, .12 Other differences between parts a and b of Figure 2 are the disappearance of the 1 4 2 5 - ~ m -band ~ and the increase of the intensity ratio I(1480)/I( 1507) in part b. Thomas and Peticolas have reported that the adenyl 1424-cm-l band is absent in a triple helix poly(dT).poly(dA)-poly(dT) with Hoogsteen type base pairing, in which the adenine N(7) and C(6)-NH2 are involved in H-bonding.,, Since this band is not affected by H-bonding at NH2,I6the disappearance of the 1425-cm-l band must be due to formation of an H-bond at N(7) that is stronger than that with water. On the other hand, the increase of I( 1480)/I( 1507) indicates strong H-bonding at C(6)-NH2, because the intensity ratio increases with increasing H-bonding strength at C(6)-NH, when excited at 266 nm7.I6It is concluded that the cAMP molecule in an aqueous CRP-cAMP complex is stabilized, at least partially, by H-bonds at N(7) and C(6)-NH,, as is found in crystalline CRP-cAMP, by X-ray crystallography.I2
1000
Figure 2. UVRR spectra of 5 5 p M c A M P (a) and a mixture of 40 p M c A M P and 65 p M C R P (b) with 266-nm excitation (1.5 mW). The binding constantslo cited in the caption to Figure 1 predict that 70% of c A M P molecules are bound to C R P in the 1:l complex form and 8% in CRP-cAMP,, and 21% are free in spectrum b.
scattering in the amide 111 region clearly becomes weak and broad, indicating partial structural change in the @-sheetpart of CRPcAMP (a cAMP band around 1250 cm-I is negligible in parts b and c of Figure 1 ) . Change in the band shape of amide 111 on going from Figure Ib to Figure I C is a result of increase and decrease in the content of CRP-CAMP, and free CRP, respectively, and suggests that the amide 111 frequency of CRP-cAMP, is also different from that of free CRP. According to the X-ray analysis of CRP-cAMP,, each of the cAMP molecules is buried in the interior of the @-rollof each subunit.12 Possibly, in solution also, the cAMP molecule is trapped in the @-rollpart of CRP and distorts the @-roll structure of the subunit. UVRR spectra of aqueous cAMP and CRP-bound cAMP excited at 266 nm are shown in parts a and b of Figure 2, respectively. Since the excitation wavelength is close to an absorption of cAMP at 260 nm, Figure 2b is dominated by the bands of the adenine ring of trapped cAMP and none of the protein bands are clearly observed. The S / N ratio of the spectrum is rather poor due to overlapping fluorescence from CRP. Certainly, however, the 1256-cm-I band of free cAMP shifts to 1245 cm-I upon complexation with CRP and the same shift is observed in a 253-nm-excited spectrum (not shown). This large downshift is not explained by H-bonding interaction between cAMP and CRP because the frequency is not very sensitive to the H-bonding state of the adenine ring.16 On the other hand, UVRR bands of adenosine in the 1250-1 150-cm-' region show large shifts on ribosyl C( 1')-D substitution (e.g., the 1253-cm-' band shifts to 1248 cm-I), which suggests that adenine vibration modes in this frequency region are coupled with the ribose ring modes and their frequencies are sensitive to the adenine-ribose glycosidic-bond conf~rmation.'~Indeed, a downshift (-5 cm-l) of the adenine Raman band at 1254 cm-I has been observed'* in conjunction with the B Z transition of poly(dA-dT) where the glycosidic-bond conformation of adenosine changes from anti to syn.I9 Hence, the downshifted frequency in Figure 2b suggests a conformational
-
(16) Toyama, A.; Takeuchi, H.; Harada, I. J . M o l . Srrucr. 1991, 242, 87-98. (17) Takino, Y. Masters Thesis, Tohoku University, 1990. (18) Taillandier, E.; Liquier, J.; Ghomi, M. J. Mol. Struct. 1989, 214, 185-21 1. Other bands of poly(dA-dT) shift on B-Z transition (e.g.. 1342-1 332 cm-I). However, we do not consider that these shifts are caused
by the antisyn conversion because the bands are insensitive to the C( 1')-D substitution of adenosine. Details were reported in ref 17. (19) Bourtayre, P.; Liquier, J.; Pizzorni, L.; Taillandier, E. J . Biomol. Struct. Dyn. 1987, 5, 97-104.
0002-7863/91/1513-3616$02.50/0
Acknowledgment. Financial support from the Ministry of Education, Science and Culture of Japan (a Grant-in-Aid for General Scientific Research, 62430004) is gratefully acknowledged. Registry No. CAMP, 60-92-4; Trp, 73-22-3. (20) (a) Clore, G. M.; Gronenborn, A. M. FEBS Lett. 1982,145, 197-202. (b) Gronenborn, A. M.; Clore, G. M. Biochemistry 1982, 21, 4040-4048. (21) Lee, B. J.; Lee, S. J.; Hayashi, F.; Aiba, H.; Kyogoku, Y. J. Biochem. (Tokyo) 1990, 107, 304-309. (22) Thomas, G . A.; Peticolas, W. L. J . Am. Chem. SOC.1983, 105, 993-996.
Selective Enrichment of the Metal Carbonyl Anion in Reactions between Metal Carbonyl Cations and Anions Yueqian Zhen, W. G. Feighery, and Jim D. Atwood* Department of Chemistry, University at Buffalo State University of New York, Buffalo, New York 14214 Received December 3, 1990 Reactions of cations and anions continue to occupy the attention of organic and organometallic chemists.'-3 Electron transfer to metal carbonyl cations from anions has been shown to occur through two mechanisms: (1) a single electron transfer that leads to odd-electron complexes and ultimately to bimetallic complexes and (2) a C 0 2 +transfer that generates a new cation and a new a n i ~ n . ~We , ~ have previously suggested that these reactions proceed by nucleophilic attack of the anion on the carbon of a carbonyl of the We now report new evidence consistent with this scheme. The reaction of Re(C0)6+ with Mn(CO)5- occurs by a single electron transfer and does not exhibit a C02+transfer? However, Re(C0)6+ Mn(CO)S+-P MnRe(CO)lo + Mn2(CO)lo+ Rez(CO)lo+ CO
+
(1) (a) Arnett, E. M.; Amarnath, K.; Harvey, N. G.; Cheng, J. P. Science 1990, 247, 423 and references therein. (b) Arnett, E. M.; Harvey, N. G.; Amarnath, K.; Cheng, J. P. J . Am. Chem. Soc. 1989, I l l , 4143. (c) Griller, D.; Simoes, J. A. M.; Mulder, P.; Sim, B. A,; Wayner, D. D. M. J. Am. Chem. SOC.1989, 111, 7872. (d) Reitstoen, B.; Norsell, F.; Parker, V. D. J . Am. Chem. SOC.1989, 111,8463. (e) Takahashi, Y.; Sankararaman, S.; Kochi, J. K. J. Am. Chem. SOC.1989, 1 1 1 , 2954. (2) (a) Lee, K. Y.; Kochi, J. K. Inorg. Chem. 1989,28,567. (b) Lee, K. Y.; Kuchynka, D. J.; Kochi, J. K. Orgonometollics 1987, 6, 1886. (c) Kuchynka, D. J.; Amatore, C.; Kochi, J. K. Inorg. Chem. 1988, 27, 2574. (d) Kuchynka, D. J.; Kochi, J. K. Inorg. Chem. 1989, 28, 855. (e) Bockman, T. M.; Kochi, J. K. J . Am. Chem. Soc. 1989, 111, 4669. (f) Lehman, R. E.; Bockman, T. M.; Kochi, J. K. J. Am. Chem. Soc. 1990, 112, 458. (3) (a) Atwood, J. D. Inorg. Chem. 1987,26,2918. (b) Zhen, Y.; Atwood, J. D. J. Am. Chem. SOC.1989, I l l , 1506. (c) Zhen, Y.; Feighery, W. G.; Lai, C. K.; Atwood, J. D. J . Am. Chem. SOC.1989, 111, 7832.
0 1991 American Chemical Society
J . Am. Chem. SOC.,Vol. 113, No. 9, 1991 3617
Communications to the Editor 0
Table I. Semiquantitative Rates of CO Exchange
II
(CO)5Re-C-Mn(C0),,
t
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-< hcterolyti c fission
-CO(from Mn)
0 I
(CO)5Re-C-Hnn(C0)5
1
-CO(from Re)
0
II
(C0)4Re-C-Mn(C0)5
1
homolytic f1ss ion
*Re(C0)5 +
*Mn(CO)g
Figure 1. Scheme suggested for interaction of Re(C0)6+with Mn(CO)
